Domain structures of (Li,Na)NbO3 epitaxial films

The domain structures of (Li_xNa_1-x)NbO₃ (x = 0, 0.05, 0.10, and 0.13) epitaxial films on SrRuO₃/(001) SrTiO₃ substrates were studied by laser scanning microscopy and reciprocal space mapping. The stripe domains with in-plane antiferroelectric polarization of an orthorhombic P phase were observed at x = 0. At x = 0.05 and 0.10, the crystal phase was changed to an orthorhombic Q phase and the domain structure was changed to a mixture of stripe domains with in-plane ferroelectric polarization and thick line-like domains with out-of-plane ferroelectric polarization. At x = 0.13, the line-like domain pattern was altered to a leaf-like domain pattern and out-of-plane ferroelectric polarization of a rhombohedral N phase was induced in the stripe domains. After an electric field was applied along an out-of-plane direction, some of the stripe domains with the in-plane polarization of the P phase at x = 0 and those with the in-plane polarization of the Q phase at x = 0.05 were switched to domains with out-of-plane polarization of the Q phase. On the other hand, stripe domains with out-of-plane ferroelectric polarization of the N phase were formed in the line-like and stripe domains of the Q phase at x = 0.10. At x = 0.13, most domains changed to stripe domains of the N phase. The relationship between the domains and the remanent polarization was discussed.